The present invention relates to an optical, light energy-transmitting device, for transmitting the illumination of a projection field and window to another one.
A device of the type to which the invention pertains is used, for example, as follows. A movie projector is usually provided with a particular window which is fully illuminated and accommodates a particular format for the frames of a film, for example, a 70 mm or a 35 mm film format. One cannot use that projector without modification for running and projecting a film of a different format. Aside from mechanical difficulties such as different requirements for the sprocket transport of the film strip, different reel sizes, etc., the illumination is wrong for a different-size frame format. One needs in particular a different window, cooperating with the different format-type film which, moreover, is also moved by its own transport. Thus, one needs adapter equipment to be placed in front of the regular window of the projector.
The invention now is specifically concerned with the optics needed to transmit or transfer the illumination field in (and from ) the original and regular window of the projector, to the window in the adapter equipment. A projector, thus modified, can then readily be used for showing, e.g., a 16-mm movie in a 35-mm projector without direct structural modification of the latter, except that the projection lens is replaced by the adapter. This adapting equipment is simply removed when the projector tube is used for showing a movie of the format for which it was designed.
Optical transmission systems for the described purpose have been used in the past, actually for quite a long time. However, there was little need for such an optical transmission system because format adaptation as described was very rare. It is a fairly recent development that the demand has increased to show, for example, a 16-mm movie (or a super 8) on a "regular" 35-mm movie projector.
The types of transmission systems for that purpose and, as they are known, appear to fall into two groups or categories to be explained briefly below with reference to FIGS. 1 and 2. Both types are characterized by a rather drastic loss in illumination intensity from the center towards the edges of the effective illumination field. Since many commonly used projectors exhibit already such a drop, particularly in the corners of the illumination field, this additional loss and drop-off in illumination deteriorates the illumination quality and distribution further which may well account for the fact that these known devices are used only with considerable reservations. Moreover, the known transmission devices and systems are usable only for a particular distance between primary and secondary windows.
Thus, there is a need to provide an optical illumination field transmitting device which does not produce dark corners in the projection field and is not constrained by fixed window spacings.